An earthquake of that size is quite strong (the Richter scale is logarithmic, with an earthquake being about thirty times stronger than an earthquake a point less), but the damage can be very minimal — even negligible — if it occurs in a sparsely populated area. Certainly the border region where North Korea, China, and Russia meet has few people, although Vladivostok up a bit further is a sizable city:
The epicenter was 42.7 degrees northern latitude and 130.9 degrees eastern longitude 110 km southwest of Vladivostok near the border of North Korea, China and Russia.With a 3.0-magnitude quake having recently hit the capital region recently, the CSI points out that the Koreas have been experiencing more and more earthquakes the past few decades (an ominous Biblical sign, by the way):
The KMA said the quake was strong but the actual surface wave magnitude was a mere 2 because it happened 562.5 km below from the surface. "It's the kind of situation where objects hanging from the ceiling swing a little and parked cars shake slightly, so almost no damage seems to have been done to people or buildings in North Korea and elsewhere," a spokesman said.
According to Chosun Ilbo's analysis of the KMA data, 157 quakes occurred in both Koreas in the 1980s, but the frequency soared to 259 in the 1990s to 436 in the 2000s. Sixty quakes were reported last year, the most in the 31 years since the KMA began observation. Eight already occurred this year, similar to last year's monthly average of five.This, of course, leads many to worry about Seoul's ability to withstand a far stronger — but also far less likely — super quake, like what hit Haiti. Robert Neff of The Marmot's Hole posted a good write-up on the prospect two weeks before the recent Seoul quake (which makes me suspect he's behind it):
South Korea has far outdistanced North Korea both in frequency and magnitude of quakes. A total of 279 quakes have been reported on the peninsula since 1978, with 199 in the South and 80 in the North. Of the five quakes stronger than magnitude 5 since 1978, four occurred in South Korea. The South also led in terms of frequency of quakes with magnitudes between 4 and 5 with 28 of all 33.
According to Yonhap - if a 7.0 magnitude quake strikes near Seoul more than 50,000 residents of the city will perish and nationwide there will be more than 670,000 casualties.Again, let me remind you that the difference between a 5.0 and a 7.0 is quite high. By way of analogy, think of a 4.0 as how far you can travel in an hour on foot, a 5.0 as how far you can travel in an hour by bicycle, a 6.0 as how far you can travel in an hour by car, and a 7.0 as how far you can travel by jet. It's not exactly like that, but you get the idea. Still, that doesn't mean the Seoul-Kyŏnggi-Inchon megalopolis is immune to super earthquakes.
The Seoul Disaster Risk Management Profile (last updated July 2006 PDF) (for those who don’t want to use PDF you can use cityriskpedia which basically has the same material) states that on October 7, 1978, a 5.0 earthquake near Hongseong damaged 1,120 buildings which inspired the Korean government in 1988 to require all buildings to withstand an earthquake of magnitude 7.
At any rate, I did wonder about the prospect of a quick and far-reaching disaster like an earthquake hitting North Korea, something along the order of the Sichuan earthquake, where the populace quickly laid blame on the authorities for not building their homes nearly as soundly as they did government buildings. Add to that the rumor mill and you could get some highly angry people with nothing to lose, especially if rumors of a government hand in the disaster were to emerge (like this).
Could an event like that be a catalyst for so much discontent that it led to regime collapse? I'm asking, not saying. Discontent might be high enough now that a massive earthquake, a Katrina-scale event, or some other quick catastrophe may be enough for order to collapse, with the regime no longer having the ability to bring things back to "normal."
And I'm certainly not wishing something like this on North Korea. Me talking about it does not make it happen; I'm only discussing the possible outcomes were it to occur.